The present invention relates to fluid flow meters, and more particularly to a pulse transmitter for a positive element or rotating-element flow meter.
A conventional class of flow meters has a rotatable component such as a spindle connected to a nutating disk. Traditionally, such meters are equipped with mechanical counters or totalizers for indicating a cumulative volume which is periodically read and recorded. In industrial process applications such as mixing batches of concrete, it is desired to continuously monitor and control the flow in order to maintain a correct mixture. Thus the meter is equipped with a transmitting device that is monitored by a computer, pulse counter or the like in an electronic control system. Rotation of the element, coupled magnetically through a wall of the meter, is transferred to an input shaft of a pulse transmitter that is fastened to the meter. The pulse transmitter is typically equipped with reduction gears for providing a calibration range and interchangeable calibration gears for making small-scale changes in the quantity of fluid metered per pulse.
The conventional pulse transmitters have one or more of the following disadvantages:
1. They are unreliable because of the excessive drag caused by a large number or range and calibration gearing elements, particularly where unity reduction or step-up gearing is required;
2. They are unreliable because of magnetic interference between the magnetic coupling and a magnetically operated switch used as the transmitting device;
3. They are expensive to produce in that a large number of transmitters having separate calibration ranges must be inventoried because the calibration gears provide a limited calibration range for each transmitter;
4. They are difficult to monitor in operation because the moving parts are not visible; and
5. Field modification of the range of calibration is impractical because difficult dissassembly and reassembly of the transmitter is required.
Thus there is a need for a pulsed flow transducer that has low rotational drag at unity reduction ratio, a large range of field-changeable calibration, and is reliable, easy to monitor, and inexpensive to produce.